1. Field of the Invention
Embodiments of the present invention relate generally to methods and systems and, more particularly, to mechanisms and techniques for electrically connecting various internal parts of a turbomachinery to an external connection.
2. Description of the Related Art
During the past years, the importance of turbomachines in various industries has increased. A turbomachine can be a compressor, expander, turbine, pump, etc. or a combination thereof. Turbomachines are used in engines, turbines, power generation, cryogenic applications, oil and gas, petrochemical applications, etc. Thus, there is a need for improving the efficiency and reliability of turbomachines.
A known turbomachine often used in industry includes a compressor driven by an electrical motor. Such a turbomachine may be employed, for example, for recovering methane, natural gas, and/or liquefied natural gas (LNG). The recovery of such gasses would reduce emissions and reduce flare operations during the loading of LNG onto ships. Other uses of this kind of turbomachine are known in the art and not discussed here.
An example of such a turbomachine is shown in FIG. 1. The turbomachine 2 includes an electrical motor 4 connected to a compressor 6. The connection between the two machine shafts can be achieved by a mechanical joint 8. The motor's external casing 10 may be attached to the compressor's external casing 12 by, for example, bolts 14. The compressor 6 may include one or more impellers 16 attached to a compressor shaft 18. The compressor shaft 18 is configured to rotate around a longitudinal axis X. The rotation of the compressor shaft 18 is enhanced by using magnetic bearings 20 and 22 at both ends of the compressor shaft 18.
However, the magnetic bearings 20 and 22 require a supply of electrical power in order to function. The electrical power is supplied to the magnetic bearings 20 and 22 via cables 24 and 26. Cable 24 connects to the magnetic bearing 20 while cable 26 connects to the magnetic bearing 22. Cable 24 is provided with a head 28 that is configured to mate with a corresponding head 30 of an external electrical cable 32. Cable 26 connects in a similar way to an external cable 34. Cables 24 and 26 are exposed to the media that is processed by the compressor. This media may be corrosive and is likely to have a high pressure and temperature. Thus, specific precautions need to be taken for protecting the cables. Cables 24 and 26 may be attached to an internal wall of the compressor casing 12. The same is true for the motor 4, in which cables 36 and 38 connect magnetic bearings 40 of the motor 4 to an outside power source.
The cables 24 and 26 are representative of conventional low voltage conduits for delivering electricity to the magnetic bearings 20 and 22. These conventional conduits are typically constructed using metallic conduits which contain electrical cables. These conduits are then filled with oil to provide both electrical insulation and to provide additional resistance to external pressures which often exist in the various working environments for the turbomachine 2. The electrical cables 24 and 26 can reside in metallic conduits, which can be flexible or rigid. An example, as shown in FIG. 2, of a flexible metallic conduit is a corrugated pipe 42. The corrugated pipe has a small thickness of sheet metal, which may be a stainless steel. Low voltage electrical connections are typically attached to each end of the corrugated pipe by welding. The corrugated pipe is then typically surrounded by a bridle 44, an example of which is shown in FIG. 3, of metal that assists in protecting the corrugated pipe from damage during assembly and operation. An example of a conventional rigid conduit is a rigid pipe which contains the electrical cables and has an electrical connector on each end of the pipe. These conventional electrical cables can generally operate in conditions of up to 125° C. and 140 bar. These conventional conduits have various considerations for use as will now be described.
Oil filled corrugated pipes 42 typically need to support external pressure applied upon them while maintaining some flexibility. This tradeoff results in thin walls to reduce stress when bending, while attempting to provide support against externally applied pressure. Handling and fabrication of the oil filled corrugated pipes is also challenging due to the small wall thickness of these corrugated pipes as well as the need to be correctly filled so as to remove the presence of gas which may generate conduit restriction when under an external gas pressure. Also the thermal gradient needs to be considered since the oil expansion from heating can also generate undesirable mechanical stress on the corrugated pipe. Additionally, for flexible pipes, which contain electrical cables, the environment within the turbomachine 2, for example, an acid or sour gas presence, may also cause failure (or premature replacement requirements) for the thin walled, flexible, corrugated pipes 42.
For rigid pipes, routing and assembly within the turbomachine 2 is generally not optimal due to the lack of flexibility of the pipes. Accordingly, it would be desirable to have other methods and systems for routing electrical cables within a turbomachine.